An important step in processing a self-developing film unit is the distribution of a fluid, preferably a liquid processing composition between and contact with opposed or superposed sheet-like elements of an exposed self-developing film unit to initiate a diffusion transfer process. In order to obtain an optimum quality positive print, the distributed layer of processing composition should cover the entire photoexposed area and be uniform in thickness.
The film unit comprises a first sheet-like element having one or more photosensitive layers thereon and a second sheet-like element having one or more image-receiving layers thereon. These first and second sheet-like elements form a laminate and the photosensitive layer or layers are exposed through a transparent section of one of the sheet-like elements. The image-receiving layer or layers are incorporated in the laminate and subsequent to the fluid distribution, the positive print may be viewed through the same transparent section of the film unit.
The film unit includes a rupturable container or pod of fluid processing composition at one end of the film unit from which the fluid is dispensed and distributed in a thin layer in response to passing the film unit's pod, between a pair of pressure applying members.
In a typical self-developing photographic system, the film units are arranged in stacked relation within a film container which is adapted to be inserted into the receiving chamber of an appropriate camera to locate the forwardmost film unit in the stack in position for exposure.
Subsequent to exposure, the forwardmost film unit is advanced through a withdrawal slot in the container, pod first, and into engagement with a pair of pressure applying members mounted within the camera. The pressure applying members exert a compressive force on the pod causing it to rupture and discharge the fluid between the predetermined adjacent layers at the leading end of the photo-exposed area. Continued advancement of the film unit between the pressure applying members results in the fluid being advanced along a liquid wave front toward the trailing end of the film unit such that it is progressively distributed over the entire photo-exposed area of the film unit.
The uniformity of the liquid layer is, to a large degree, determined by the initial shape of the liquid wave front. In order to uniformly spread the processing composition over a substantially rectangular or square photo-exposed area, it is preferable that the wave front be disposed in a substantially straight line which extends outwardly to the lateral margins of the area and is oriented in a direction that is normal to the direction of film advancement between the pressure applying members.
There are several factors which affect the initial shape of the wave front. One is a design of the pod and its rupture characteristics. Another relates to the viscosity and amount of liquid enclosed by the pod. The wave front shape is also influenced by the velocity at which the film unit is advanced through the pressure applying members, the amount of compressive pressure exerted on the film unit, and the resistance to fluid flow at the interfaces between the liquid and the predetermined layers.
One of the most commonly observed spread shapes is a tongue shape wherein the wave front progresses towards the trailing end more rapidly in the central portion of the photo-exposed or image-forming area than out at the lateral margins. This condition is most likely caused by the relatively low resistance to fluid flow at the center of the film unit compared to the flow resistance at the lateral margins or outer (off-center) portions of the image area. The difference in the flow resistance can be attributed to the fact that the lateral edges of the superposed sheet-like elements are held together by binding tape or structure within the camera while the central portion of the sheets are not so restrained and may more easily separate or delaminate to accommodate the mass of fluid discharged from the pod.
Due to the concentration of fluid at the center of the film unit, it is possible that the corners at the rear or trailing end of the image-forming area may not be completely covered during the subsequent spreading operation.
One method employed to compensate for the tongue-shaped wave front has been to equip the camera or film container with spread control devices which serve to modify the shape of the liquid wave front during spreading.
The spread control devices are designed to apply a second compressive force to the central portion of the film unit in the path of the mass of fluid discharged from the pod by the pressure-applying members. This serves to selectively reduce or limit the separation or gap between the adjacent layers and retard the central portion of the wave front thereby causing a flow of liquid in a direction transverse to the direction of film advancement. In this manner, the wave front is modified such that it is substantially straight and is oriented in a direction substantially normal to the parallel lateral sides of the rectangular or square image-forming area.
For examples of cameras and film cartridges which are equipped with devices for controlling the distribution of liquid processing composition, reference may be had to Kinsman, U.S. Pat. No. 3,832,731, entitled "Photographic Film Assemblage", and Friedman, U.S. Pat. No. 4,104,669, entitled "Photographic Processing Apparatus", both of which are assigned to the same assignee as the present invention and are incorporated herein by reference.
As disclosed in Bendoni, U.S. Pat. No. 4,087,831, entitled "Bearing Block Mount for a Photographic Fluid Spreading Apparatus" assigned to the same assignee as the present invention, it is well known in the art that the speed at which the film unit is progressively advanced between the rollers critically effects the distribution of the fluid processing composition between the superposed elements i.e., the thickness of the layer of the processing composition and thereby the final development of the photographic print. For example, if the film unit is advanced too rapidly between the rollers, the layer of processing composition deposited between the superposed elements may be too thin and result in a poor quality photographic print. Furthermore, if the film unit is advanced too slowly, the distribution of the processing composition between the superposed elements may be incomplete as the limited supply of fluid included in the container may be exhausted before the processing composition has been uniformly distributed in a layer between the superposed sheet elements. For instance, one of the major drawbacks in producing a self-developing camera of the type in which the film unit is manually withdrawn between the spreader elements is the inability to establish the highly unpredictable linear rate at which the film unit shall be withdrawn between the rollers by the operator. Typically, the desired linear rate or pull rate at which the film unit should be withdrawn between the rollers is within the range of 6 to 9 inches per second. However, it has been established that operators generally pull film units as rapidly as 105 inches per second and as slowly as 3 inches per second with a greater majority of the operators pulling the film unit at a rate exceeding 50 inches per second.
Similarly, if the camera is of the single lens reflex type, the complete operating cycle (which consists of converting the optical system from the viewing mode to an exposure mod) may occur in as little as 1.5 seconds, as discussed in Johnson, et al., U.S. Pat. No. 4,047,192, entitled "Photographic Apparatus with Sequencing System" assigned to the same assignee as the present invention.
It is stated in Takimoto, U.S. Pat. No. 5,032,911 entitled "Video Image Printer Using Liquid Crystal Light Valves and Primary Auxiliary Direction Scanning", that a printer is coupled to a video camera wherein the film is exposed successively line by line, and is introduced between the squeezing rollers in synchronism with exposure of the film. The Takimoto patent further states that the squeezing rollers serve as a means for spreading processing solutions, and pressing the film there between, while at the same time feeding the film in the auxiliary scanning direction. The Takimoto patent fails to disclose, among others, how the spread process is accomplished.
Moreover, the Takimoto camera and printer are built as an integral unit and both must be carried into the field together whenever the camera is used even though the camera user may not actually desire hard copy prints in the field.
As disclosed in Finnelli et. al., entitled "Electronic Camera System with Detachable Printer", assigned to the same assignee as the present invention and herein incorporated by reference, an electronic imaging system comprises a camera and hard copy printer which can be interconnected for use either in combination or apart. While Finnelli imaging system is entirely satisfactory from a performance standpoint, it does not specifically disclose how the spread process is accomplished.
The primary objects of the present invention is to provide a compact and portable handheld imaging system comprising both an electronic camera and electronic photographic printer separately housed and readily interconnectable for selective use either together or apart; and wherein the processing fluid spread system spreads the processing fluid on an advancing film unit without interfering with a stationary print head that is simultaneously exposing the advancing film unit by emitting consecutive lines of image bearing light on the film unit.
In particular, the print head is stationary while the film unit is advanced proximately thereto. Once the initial lines on the leading side of the film unit has been exposed then the fluid spread system begins to spread the processing fluid in a thin layer between the sheet elements, while simultaneously the trailing portion of the film unit continues to be exposed. In one embodiment of the present invention, the exposure time (i.e., the interval from the time the film unit is picked to completion of the film unit ejection) shall be less than 15 seconds which equates to approximately 0.37 inches per second. Since the advancing film unit is simultaneously exposed and photographically processed the fluid spreading rate is determined by the optimum exposure rate, i.e., 0.37 inches per second. This rate of processing the film unit is considerably slower than any of the other known prior art, or prior art discussed above. This specified unconventional slow rate of film exposure and advancement should be considered illustrative for the purpose of discussing the embodiments herein. Various ranges that may be approximate to this specified rate (either greater or lesser) should be included as well.
Another concern of the present invention is preventing the liquid wave front caused by the ruptured container from encroaching on the line of exposure emitted by the print head on the advancing film unit. Thus, the permitted wave front of the present invention is significantly less than the wave front of the prior art to prevent the processing fluid from covering areas of the film unit that have not yet been exposed.
Thus, more primary concerns of the present invention involves providing a compact and portable handheld imaging system comprising an electronic camera and electronic printer useable either apart or in connection with respect to each other wherein the printer can provide a high quality photographic print of the image recorded in the camera; wherein the stationary print head effects progressive exposure on the advancing film unit simultaneously as the fluid spread system spreads the processing fluid over the film unit to effect processing of exposed portions of the film unit.
There is therefore a need in the art for an effective photographic processing fluid spread system that can process an advancing film unit that is simultaneously and progressively being exposed by a print head. Particular need remains for a photographic processing fluid spread system that can control the thickness of the processing fluid layer in a uniform manner, as well as restrict the associated wave front of the processing fluid as the film unit is advanced at rate considerably slower than the conventional art.
Of course, the above objectives and concerns need to be addressed in an imaging system that would be suitable for portability wherein the system weight is minimal and the system is not susceptible to shock, vibration, and gravitational orientation while in the operating or non-operating modes.